This invention pertains to sewing machines; more particularly, to a low friction throat plate for use in a sewing machine having an above the bed feeding system.
In the heretofore known sewing machines having above the bed feeding systems, there is provided a presser foot for clamping the work material in position against the thrust of the sewing needle and a feeding foot for moving the work material when the sewing needle is removed therefrom, the presser foot and the feeding foot operating alternately and in synchronism with end-wise reciprocation of the sewing needle. Such a device is shown in the U.S. Pat. No. 3,808,994 issued on May 7, 1974 to Kuhn.
It is also known, in bottom feed sewing machines where the material is fed through the sewing machine by a feed dog extending up through a throat plate, that the bottom piece of work material may undergo greater motion than the top piece of work material resulting in a mismatch between the materials at the end of the seam. It is easy to understand that a similar situation may ensue with a top feeding system in that drag of the lower piece of work material upon the throat plate will cause a similar problem with seam end equalization.
To combat some of the above problems, sewing machines have been produced with combined upper and lower feeds. Typically, in these sewing machines, the lower feed dog operates in opposition to the upper feeding foot, which particularly at high speed may produce a floating of the upper feed recoiling from the feed dog, whereby work material lying in between the feed dogs and feeding foot is not positively driven.
What is required in some means for efficient feeding of work material without the problems and cost attendant upon opposing feeding elements and without the drag imposed upon one ply of work material laying adjacent a static member.